The methods available to those who worked in psychology's first laboratories were relatively limited. While considerable progress had been made in designing apparatus to control the systematic presentation of stimuli, to measure the time taken by or strength of an observer's reactions, and even to register the duration or course of response for later analysis, use of this apparatus was generally restricted to the study of sense perception and reaction time. Stimuli were relatively simple (e.g., a flash of light, a sound of a given frequency or amplitude, pressure from a weight of known mass or from two points at varying distances from one another, chemical odors) and the observer's response typically involved a simple judgment or movement, possibly accompanied by introspection regarding the experience itself.

In 1885 a monograph from the pen of a young psychologist, Hermann Ebbinghaus,[1]opened a new vista on experimentation. Published in German as Über das Gedchtnis and eventually translated into English as Memory. A Contribution to Experimental Psychology,[2] this monograph marked the beginning of programmatic experimental research on higher mental processes. Using himself as a subject, gathering data for over a year (1879-80), and then replicating the entire procedure (1883-4) before publishing, Ebbinghaus not only brought learning and memory into the laboratory, he set a standard for careful scientific work in psychology that has rarely been surpassed.

In order to proceed with his research, Ebbinghaus had first to invent stimulus materials. These needed to be relatively simple, neutral as to meaning, and homogeneous. They needed to be available in large numbers and to allow quantitative manipulation of the amount of material to be retained. In answer to these needs, Ebbinghaus hit upon the idea of a 'nonsense syllable.' As he described it: 'Out of the simple consonants of the alphabet and our eleven vowels and diphthongs all possible syllables of a certain sort were constructed, a vowel sound being placed between two consonants. These syllables, about 2,300 in number, were mixed together and then drawn out by chance and used to construct series of different lengths, several of which each time formed the material for a test.'[3]

Next Ebbinghaus had to develop novel methods for controlling the degree of learning and measuring the amount of retention. At first glance, it would seem that the most obvious method for controlling learning would have been to standardize the number of learning trials. The problem with this method, however, is that the degree to which any given material is learned in a fixed number of trials may vary as a function of the material or the mental state (e.g., attention, fatigue) of the learner. To circumvent this limitation and assure that material was learned to approximately the same degree from test to test, Ebbinghaus introduced the method of learning to criterion. In learning to criterion, the subject repeated the material as many times as was necessary to reach an a priori level of accuracy (e.g., one perfect reproduction).

Measuring the amount of retention also presented Ebbinghaus with a puzzle. Because it is influenced by whole host of factors, conscious recall of material can vary from moment to moment even when the material has been well learned; worse yet, material may not be available to conscious recall at all even though it has been retained to some degree. To avoid this problem, Ebbinghaus invented the 'savings method'. Subtracting the number of repetitions required to relearn material to a criterion from the number originally required to learn the material to the same criterion provided an index of retention that was independent of whether the material could be consciously recalled.

With these methods, Ebbinghaus obtained a remarkable set of results. He was the first to describe the shape of the learning curve. He reported that the time required to memorize an average nonsense syllable increases sharply as the number of syllables increases. He discovered that distributing learning trials over time is more effective in memorizing nonsense syllables than massing practice into a single session; and he noted that continuing to practice material after the learning criterion has been reached enhances retention.

Using savings as an index, he showed that the most commonly accepted law of association, viz., association by contiguity (the idea that items next to one another are associated) had to be modified to include remote associations (associations between items that are not next to one another in a list). He was the first to describe primacy and recency effects (the fact that early and late items in a list are more likely to be recalled than middle items), and to report that even a small amount of initial practice, far below that required for retention, can lead to savings at relearning. He even addressed the question of memorization of meaningful material and estimated that learning such material takes only about one tenth of the effort required to learn comparable nonsense material.

Finally, in the treatment of his results, Ebbinghaus made considerable use of mathematics. He not only assessed statistical significance but characterized his findings in mathematical terms. Given this quantitative treatment, Ebbinghaus's methodological innovations, and the care with which he carried out his research, it is not surprising that his results have stood the test of time. Indeed, in the century since the publication of his monograph, surprisingly little has been learned about rote learning and retention that was not already known to Ebbinghaus.